1. Field of the Invention
The present invention generally relates to a chuck for holding and positioning semiconductor workpieces during various processing procedures, and more particularly relates to a vacuum chuck for holding and positioning the semiconductor workpieces more stably and securely.
2. The Related Art
In a semiconductor device manufacturing process, semiconductor workpieces such as wafers need to undergo various processing procedures. The wafers are usually held and positioned on a chuck to be processed and the chuck is an important device in the semiconductor device manufacturing process.
With the development of semiconductor technology, the chuck is improved gradually for satisfying the requirement of the various processing procedures. The chucks are divided into two kinds. One kind is a contact type chuck and the other kind is a non-contact type chuck. A vacuum chuck which holds and positions the wafer thereon by vacuum drawing force is a typical contact type chuck. Referring to U.S. Pat. No. 6,032,997 discloses a vacuum chuck. The vacuum chuck has a body portion. The body portion defines a top surface. A plurality of concentric flat lands are disposed on the top surface. Between every two adjoining lands, a concentric trench is defined. Several orifices are defined to pass through the body portion and communicate with the trenches respectively. Each orifice is connected to a vacuum hose which is connected to a vacuum source. The wafer contacts the lands and then the air is evacuated from the trenches. Lastly, the wafer is held on the lands of the vacuum chuck by the vacuum drawing force.
Another vacuum chuck is published in U.S. Pat. No. 6,164,633. The vacuum chuck has a generally square body. The body has a first surface and a second opposing surface. The first surface has a first circular platform and a second circular platform for receiving two different diameter wafers. The second surface has a third circular platform for receiving a wafer having a third diameter. A first vacuum trough and a second vacuum trough are respectively formed in the first platform and the second platform. A third vacuum trough is formed in the third platform. Three vacuum passageways are formed and extend from the interior portions of the body to three exterior vacuum ports located at one side of the body. Each vacuum passageway corresponds to a single vacuum trough and links the respective vacuum trough to a vacuum source and so that the air is evacuated from the vacuum trough to hold the wafer on the corresponding platform.
However, the two vacuum chucks disclosed above have very weak airtightness, which easily causes the wafer held thereon to come off the vacuum chuck and damage the wafer.